Question

When the direction of nerve impulse is reversed, the condition is-
a. Axo-Axonic synapse
b. Axo-Dendritic synapse
c. Both of the above
d. None of the above

Answer 1

Hint: The path of nerve impulse is either from axon to dendron or from axon to axon, when the nerve impulse produced in the neuron. A nerve impulse can move in only one direction within a chemical synapse.

Complete answer:
> Option A is correct. An axo-axonic synapse is a type of synapse that is created by one neuron projecting its axon terminals onto the axon of another. Presynaptic neurons release chemicals at axoaxonic synapses to modify the behaviour of terminal ends (synaptic knobs) on the postsynaptic neurons. Therefore, the release of neurotransmitters is either encouraged or prevented when an action potential arrives at the terminal.
> Option B is incorrect. Many presynaptic neurons synapses around the postsynaptic neuron's dendritic spines. This form of touch is called axo-dendritic synapse because of the position. At axodendritic synapses, the chemicals produced by presynaptic neurons excite or inhibit the postsynaptic neuron's dendrites and cell body. If adequately stimulated, the axon of the postsynaptic neuron will produce an impulse or potential for action.
> Option C is incorrect. The direction of the nerve impulse depends upon the source/origin and destination/end of the nerve impulse. Therefore, only one of the above options is correct.
> Option D is incorrect. This option is not possible when the direction of the nerve impulse is clearly mentioned in the given options. Hence, there should be one correct option of the following two options given above.

Additional information:
Synapse is the position where electrical nerve impulses are transmitted between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). The neuromuscular junction in which neural impulses are transmitted by chemical means between two neuronal processes or between a neuron and an effector organ. The impulse induces the axon terminal presynaptic membrane to release a neurotransmitter (e.g., acetylcholine, or norepinephrine). The neurotransmitter molecules are diffused through the synaptic cleft, binding to the postsynaptic membrane with different receptors, causing the postsynaptic cell to depolarize or hyperpolarize. A nerve impulse may move in only one direction within a chemical synapse. By comparison the impulse travels in both directions in an electrical synapse. During this phase, the nerve impulse path is reversed from axon to dendron, to axon to axon.

>So, the correct answer is Option A.


Note: The presynaptic neurons will reach and communicate with postsynaptic neurons in the central nervous system, where most synapses occur. Depending on the position of the synapse (i.e. the axonal or dendritic terminal of the neuron), there are different forms of synapse (such as axo-axonic synapse, axo-dendritic and axo-somatic synapse).